This invention relates to systems for suppressing motion or vibration, and more particularly to self-adjusting systems adapted for use on remote systems such as spacecraft.
Modern spacecraft often carry instruments that must be pointed toward targets with an accuracy less than 1 minute of arc. Spacecraft attitude control systems are able to achieve such accuracies. Often, however, the instruments are mounted on arms or booms extending from the spacecraft body. Vibrations of the arms may directly perturb the instrument pointing. The bandwidth of the attitude control system may be insufficient to damp vibratory motions, and in any case, cannot cope with pointing inaccuracies resulting from flexural vibrations.
Many sources of motion or vibration exist on modern spacecraft: actuators, momentum wheels, scanning instruments, articulating antennas, tape recorders and the like, all of which may contribute vibrational disturbances.
Passive and active vibration damping systems are well known for suppressing such induced vibrations. Passive systems include dashpots with viscous liquids, which, however, tend to be temperature sensitive and heavy. An active system is described, for example, in U.S. Pat. No. 4,922,159, issued May 1, 1990 in the name of Phillips et al. Active systems include a sensor for measuring vibration, a proof-mass actuator coupled to a vibrating body, and a feedback loop for tending to reduce the unwanted motion.
Active dampers, such as that described in the abovementioned Phillips et al. patent, include feedback loops which tend to be make the disturbance rejection capability frequency sensitive. When a spacecraft includes many potential sources of vibration representing a wide spectrum of frequencies, a single active damping system is incapable of simultaneously performing effective damping of all the vibrations.
Weight considerations preclude the use of a large number of such active dampers in spacecraft applications to damp vibrations of different frequencies. Even if it were possible to include several active vibration dampers on a spacecraft, they might still not provide adequate damping because the vibration modes are time varying, and depend inter alia on temperature and rotational velocity.
An improved motion suppression system is desired.